Some monster abilities will hit multiple characters, so long as they are in front of the mob. "In front" generally means the 45° arc in the direction the mob is facing, although this can vary, along with the length of the cone, depending on the monster and ability being used. If the ability does damage, the targets will take less damage the further they are from the middle of the cone. See also, Area of Effect, for more information about cone attacks and other AoE types.